Energy conversion devices



Sept. 20, 1966 T. J. SWOBODA 3,274,405

ENERGY CONVERSION DEVICES Filed March 17, 1964 5 Sheets-Sheet 1 FIG-I le'o.

1 42 52 INVENTOR THOMAS J, SWOBODA BY %7 ym ATTORNEY Sept; 20, 1966 Filed March 17, 1964 RESISTWITY (HICROOHN-OM.)

T- J- SWOBODA ENERGY CONVERSION DEVICES 5 Sheets-Sheet 2 FIG. ]Z[

CHANGE IN RESISTIVITYON HEATING DIMENSIONAL CHANGE 0N HEATING Y INVENTOR THOMAS J. SWOBODA ATTORNEY TEMP C) United States Patent 3,274,405 ENERGY CONVERSION DEVICES Thomas J. Swoboda, Chester County, Pa, assignor to E. L du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware Filed Mar. 17, 1964, Ser. No. 352,539 12 Claims. (Cl. 310-4) This invention relates to devices for the interconversion and control of various forms of energy based on ferromagnetic compositions having a maximum saturation induction within a restricted temperature range and a very much smaller induction at temperatures both above and below this range.

This application is a continuation-in-part of my copending application Serial No. 181,629, filed March 22, 1962, now US. 3,126,492, which is a cont-inuation-in-part of my earlier applications Serial Nos. 776,098, filed November 24, 1958 and now abandoned; 19,370, filed April 1, 1960 and now abandoned; 66,194, filed October 31, 1960, now US. 3,126,345; and 125,511, filed July 20, 1961 and now abandoned.

The usual ferromagnetic materials retain their ferromagnetic behavior down to very low temperatures, i.e., temperatures as low as the boiling point of liquid helium and below, and are characterized by a mangetic response that decreases as temperature is increased so that above a certain temperature, know as the Curie temperature, the response becomes that of a paramagnetic material. Such materials have been employed in devices whose operation involves transformation of energy from one form to another. Certain of these devices, such as the common household thermostat based upon a bi-metallic temperature responsive element, often employ a permanent magnet as an accessory to improve performance. In devices of another type, the magnetic element itself is primarily responsible for operation. Among such devices are the motor of Van der Maas and Purvis [Am. J. Phys., 24, 176 (1956)] and the thermoelectric generator of of Schwarzkopf (US. 2,016,100). The mode of operation and manner of construction of such devices is influenced by the fact that for most ferromagnetic materials, saturation decreases monotonically with increasing temperature up to the Curie point.

It is an object of this invention to provide novel devices for the interconversion and control of various forms of energy. A further object is to provide such devices based upon compositions which exhibit a maximum saturation induction in a restricted range of temperature and a much lower saturation induction at temperatures both above and below this range.

These and other objects of this invention are obtained by providing novel devices which produce useful work in the form of mechanical or electrical energy from enorgy in the form of heat. The devices depend for their operation upon a component which exhibits a sharp and reversible increase in saturation induction over a narrow temperature range below the Curie point. Over this narrow temperature range, the mid-point of which is called the transition temperature, the component undergoes a reversible first-order solid-phase-to-solid-phase transition with maintenance of crystal symmetry. Hence this component, sometimes called hereinafter the transition material is characterized by a sharp change in magnetic saturation induction, dimension and electrical resistivity at the first-order transition temperature, as the temperature of the transition material increases or decreases through the narrow transition temperature range.

By providing the devices of this invention with means responsive to the change in magnetic saturation induction, dimension or electrical resistivity, work in the form of mechanical or electrical energy is produced.

'ice

Thus, the devices of this invention have at least two components (a) the transition material, and (b) means to translate the magnetic, dimension or electrical resistivity change of the transition material into mechanical or electrical work.

Some of the devices of this invention will have additional components, e.g., a source of heat energy for flow of heat to and from the transition material to cause the temperature of the transition material to pass through the first-order transition point. Other devices of this invention, such as temperature measuring devices, need no source of heat energy as a part of the device, for they will depend upon the heat energy of the medium in which the temperature is to be measured for the source of heat.

For better understanding of the present invention, together with other and further objects thereof, reference is made to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. I is a schematic representation of a magnetic switch;

FIG. II is a partially schematic representation of a device for measuring radiation intensity according to the present invention;

FIG. III is a partially schematic representation of a reciprocating engine;

FIG. IV is a partially schematic representation of a magnetic balance;

FIG. V is a plot showing dimensional changes brought about by heating and/ or application of a magnetic field which occur in a representative composition useful in devices of this invention;

FIG. V1 is a plot showing the change in resistivity on heating with or without application of a mangetic field for a representative material useful in devices of this invention;

FIG. VII is a partially schematic representation of a resistor according to the present invention;

FIG. VIII is a schematic representation of an alarm circuit employing a temperature-responsive magnetic switch according to the present invention;

FIG. IX is a schematic representation of a variable condenser, while FIG. X is a :graph of the effect of temperature upon the resonant frequency of a circuit using the variable condenser.

The substances employed as transition material in the devices of this invention are possessed of the characteristic of abruptly changing in a controllable manner their saturation induction, with changing temperature, from a nonmagnetic to a magnetic state in the course of the first-order transition from one solid state phase to a second solid state phase. It is preferred that this change be from an antiferrimagnetic state on the one hand to a ferromagnetic or ferrimagnetic state on the other.

A first-order transition is one in which a discontinuity occurs in the first derivatives of the Gibbs free energy function. For example, there are discontinuities in the first derivative with respect to temperature, i.e., entropy, with respect to pressure, i.e., in volume, and for a magnetic material with respect to magnetic field, i.e., in magnetization. This first-order transition is not to be confused with a second-order transition. In a second-order transition, the energy, volume, and magnetization change continuously but the temperature derivatives of these quantities have singularities. The Curie point in a magnetic material is an example of a second-order transition.

Further discussion of firstand second-order transi tions is found in Swalin, Thermodynamics of Solids, John Wiley & Sons, Inc., New York, 1962, pp. 7273 and in Phase Transformations in Solids (Symposium at 0 Cornell University, August 23-28, 1948), John Wiley &

Sons, Inc., New York, 1951, Chap. I, by L. Tisza, pp. 1-2.

Preferred first-order transition materials used in the devices of this invention are solid compositions in which the transition is solid-phase-to-solid-phase with maintenance of crystal symmetry. Such materials showing a change in saturation induction of at least five-fold and particularly ten-fold are especially preferred.

Materials useful as the first-order transition material of this invention include a variety of materials.

For example, compositions described in copending US. Patent 3,126,347, by T. J. Swoboda are useful. These compositions contain (a) at least two transition elements from the Periodic Table Groups V-B, VI-B and VII-B, i.e., V, Cr, Mn, Nb, Mo, Ta, W, and Re, of which at least one of said two elements is from the first row of said transition elements, i.e., V, Cr, and Mn, and ('b) at least one Group V-A element selected from As or Sb, which constitutes -40 atom percent of the total composition, and preferably 5-35 atom percent. Nitrogen, phosphorus and bismuth may also be present. The compositions may contain other elements from Groups II-IV in an amount not more than 30 atom percent. Such elements include cadmium, gallium, indium, lead, thallium, tin, zirconium, scandium, yttrium, magnesium, and zinc. Ordinarily one of the transition metals enumerated above will constitute the major proportion of the transition metal content of the composition while the second transition metal will be present in minor proportion. However, in no case will the content of the second transition metal be less than 0.1 atom percent based on the total composition. The Periodic Table referred to herein is the one appearing in Demings General Chemistry, John Wiley & Sons, Inc., 5th Ed., Chap. 11.

Iron-rhodium alloys (Fe-Rh) and iron-rhodium alloys containing up to atom percent of at least one other element (Fe-Rh-M) are also useful as the first-order transition material used in the devices of this invention. Suitable Fe-Rh alloys include those described by Fallot, Revue Scientifique 77, 498 (1939); and Kouvel et al., General Electric Research Report No. 61-RL-2870M. Suitable Fe-Rh-M alloys are described in copending US. applications Serial Nos. 177,229 and 177,230, filed March 5, 1962 by P. H. L. Walter, now US. 3,140,941 and US. 3,140,942, respectively; application Serial No. 192,- 060, filed May 3, 1962 by P. H. L. Walter, now US. 3,144,325; and application Serial No. 192,059, filed May 3, 1962 by T. A. Bither, now US. 3,144,324. These latter compositions may be represented by the formula Fe Rh [xM],, wherein M represents (1) at least one element selected from berylllium, magnesium, aluminum, gallium, indium, silicon, germanium, tin, lead, phosphorus, arsenic, antimony, bismuth, sulfur, selenium, or tellurium, and x is an integer from 1-6 and generally 1-2; (2) at least one transition metal of atomic number 39-44, 46-48 and 57-80, inclusive, and x is an integer from 1-6 and generally from 1-2; (3) at least one transition metal of atomic number 21-25, 27-30, inclusive, and x is an integer from 1-6 and generally 1-2; or (4) at least one rare earth metal of the lanthanum or lanthanide series of the Periodic Table of the elements of atomic numbers 58-71, inclusive, and x is an integer from 1-14, and generally 1-3. In all these iron-rhodium-metal alloys, a and b, which can be alike or different, are numbers ranging from 0.8-1.2, and c is a number ranging from 0.01-0.20, and in the instance when x is 2, the requisite cs can be alike or different but still must fall in the indicated range. These subscript numbers refer to the atomic proportions of the elements in the final alloy. M can be different within the same defined group when x is greater than 1.

Further compositions which can be employed as the first-order transition material in devices of this invention are those having a tetragonal crystal structure and containing manganese in an amount of at least 40 atom percent, a second metallic component selected from iron,

cobalt, nickel, copper, and zinc, in an amount of 0.6-25 atom percent, and at least one of arsenic, antimony and bismuth in an amount of 25-40 atom percent. Additional components selected from the elements of Groups III-A, III-B, IV-A, or IV-B, in an amount of 0-25 atom percent may also be present. These compositions are described more fully in copending US. patent application Serial No. 66,194, filed October 31, 1960 in the name of T. J. Swoboda, now US. 3,126,345.

Still other compositions useful in the present invention are described in application Serial No. 66,195, filed October 31, 1960 in the name of T. A. Bither, now US. 3,126,346. These compositions have a 'tetragonal crystal structure and contain a single transition metal selected from chromium, manganese, iron, cobalt, or nickel in an amount of 61-75 atom percent, and from 25-39 atom percent of at least two elements selected from gallium, germanium, selenium, tellurium, arsenic, antimony and bismuth, of which at least the major atom percent consists of arsenic, antimony, and/or bismuth.

Still other useful compositions can be represented by the formula Mn T' T Sb In,, where T is chromium and/or vanadium, T" is one or more of iron, cobalt, nickel and copper, x is 0.003-0.25, y is 0.003-0.25, z is 0.50-1.00 and a is 0-0.50. These compositions are more fully described in application Serial No. 261,784 of W. W. Gilbert and T. J. Swoboda, filed February 28, 1963, now US. 3,241,952.

Processes for preparing many of the compositions use ful as the first-order transition material of this invention are described in the foregoing applications and in application Serial No. 120,679 of W. W. Gilbert, filed June 29, 1961, now US. 3,196,055.

The range of temperature over which the change in saturation induction occurs can readily be minimized by preparing the composition in single crystal form or by quenching and annealing as taught by W. W. Gilbert in aforesaid application Serial No. 120,679, filed June 29, 1961, now US. 3,196,055. This process involves quenching the molten composition to a temperature below its solidification temperature, annealing at a higher temperature below the solidification temperature and cooling slowly. Optionally, a chalcogen-reactive reagent, e.g., aluminum, may be added to the molten composition prior to quenching.

Although as indicated the specific compositions described above exhibit properties which render them particularly useful in the energy transducing devices of this invention, it will be appreciated that any material exhibiting such properties can be used as the basic component of these devices.

Certain of the novel devices of this invention employ a composite magnetic component consisting of a magnetic material of the type described above (first element) in combination with a magnetic material of the usual type, viz., a material whose magnetic response is high at temperatures below a limiting temperature termed the Curie point and is zero at higher temperatures (second element). By suitable choice of these elements, composite magnetic components can be constructed which exhibit a pronounced maximum in saturation induction over a narrow temperature interval and much lower saturation induction at both lower and higher temperatures. Composite components whose saturation induction is a minimum within a narrow temperature range or is substantially constant over a desired temperature range can also be constructed. The magnetic elements making up the composite component can be united in any manner which does not disturb their individual magnetic characteristics, e.g., by lamination of sheets, butting of massive forms, compaction of powder mixtures and the like.

When a composite magentic component is employed, the second ferromagnetic element, i.e., the element exhibiting conventional dependence of saturation induction on temperature is selected on the basis of its Curie point and saturation induction in relation to the lower transition temperature and saturation induction of the first component. The position and magnitude of the temperature range over which the composite component exhibits maximum or minimum saturation induction depends on the relative temperatures at which the Curie point and lower transition point occur. For example, a composite com ponerlt made up of manganese germanide (Curie point 40 C.) and manganese-chromium-indium antimonide having a lower transition temperature of 40 C. exhibits a pronounced minimum in saturation induction at about 40 C. By suitable adjustment in the relative amounts of manganese germanide and quaternary antimonide employed in this composite, the saturation induction at temperatures above about 80 C. can be made equivalent to, higher than, or lower than the saturation induction at temperatures below about 25 C.

In the novel devices of this invention, the elements which provide heat to the transition material, which magnetize and demagnetize the transition material and which collect and detect the new form of energy produced are conventional in the art. For example, by introducing a ivotal element, with a transition material as just described, in a magnetic field and having means for magnetizing the transition material, the pivotal element can be caused to move in said field. In this way, mechanical work can be done. The pivotal element can be an armature, an oscillating arm, or a metering device. Motion can also be obtained by exploiting thermal expansion properties of the exchange inversion material.

The devices of this invention are illustrated by the following examples:

EXAMPLE I This example illustrates the use of a manganese-chromium-indium antimonide as the transition material used in the construction of a thermomagnetic generator. A flat disk /2" in diameter and 0.045 thick was prepared from a manganese-chromium-indium antimonide represented by the formula Mn Cr lIn Sb having a first-order transition temperature somewhat above room temperature by pressing in a mold under a pressure of about 30,000 psi. at room temperature. This disk was placed across and in contact with the poles of a magnet having a field strength of about 1000 gauss. magnet was employed with rectangular pole faces, each 1.4 x 1.6 cm. in dimension. The distance between adjacent edges '(the 1.4 cm. edges) of the pole faces was 1.0 cm. The maximum dimension of the magnet perpendicular to' the plane of the pole faces was 3.8 cm. A coil consisting of 300 turns of No. 44 enameled copper wire was wrapped around a section of the magnet equidistant from the pole faces and connected to a microvolt amplifier which in turn was connected to a recorder. The disk was heated above the first-order transition temperature by illumination with a beam of light produced by a microscope illuminator having a 108-watt lamp. By means of a manually operated shutter, periods of illumination about 10 seconds in length were alternated with periods of about equal duration during which the light beam was interrupted. Variations in voltage of 7 microvolts occurred corresponding to the variations in light intensity.

EXAMPLE II This example illustrates the use of a manganese-chromium-indium antimonide as the transition material used in the construction of a solar motor operating on a heating and cooling cycle in the region of the lower transition temperature. This motor possesses an advantage over similar motors constructed from conventional magnetic materials in that the magnetic material can be selected to have a sharp transition in a desired temperature range thereby permitting most efiicent use of the heat available.

A disk approximately 2" in diameter was carefully cut from a thin mica sheet and a small hole drilled through A U-shaped (horseshoe) 6 the center. Through this hole a thin glass tube was passed perpendicular to the plane of the disk to serve as a bearing. The disk was fastened to this tube with cement. An axle was placed within the tube and supported at the ends.

Transition material particles represented by the formula Mn Cr In Sb were adhered at the edge of each face of the disk in a band Ms" wide by means of silver paste of the air-drying ty-pe. lAfter thorough drying, the rim of the disk was coated with soot from a small candle to enhance heat absorption.

The stator of the motor was a magnet having a field strength of 4800 gauss with facing pole pieces approximately in diameter and apart. The axle was mounted in a horizontal posit-ion parallel to and about 1 /2 away from the center line of the pole pieces with the plane of the mica wheel centered in the gap. A beam of light from a lamp consuming 6 amperes at 6 volts was focused so that an image of the filament was produced on each side of the rim of the wheel at a position just above the magnet poles. When the light Was turned on, the wheel rotated steadily making a complete revolution in sligthly less than one minute. This motor readily raised a mass of 255 mg. mounted at a distance of 2 cm. from the center of rotation.

In place of the lamp, sunlight was focused onto the wheel using a spherical lens of 8 /2 in. principal focal length and 3%" in diameter. In order to prevent over heating, the image of the sun was defocused somewhat and only about half of the area of the spot impinged on the Wheel. Under these conditions, the motor turned readily and raised the 255 mg. weight in about 18 seconds.

EXAMPLE III This example illustrates the construction of a magnetic switch useful in automatic control and alarm devices.

A flexible brass reed 4 of FIG. I measuring .008 thick x & Wide x %1" long was firmly mounted at one end so that the free end was adjacent to the poles of a horseshoe magnet 5. To this end were attached electrical contacts, normally closed, and a small piece of transition material (manganese-chromium-indium antimonide 6) prepared from a mixture containing these elements in the atomic proportions l.8:0.2:0.l5:0.85. (This antimonide exhibited a lower transition temperature of about 40 C. and a maximum saturation induction at about C.). When the antimonide was warmed above 40 C., it was attracted to the poles of the horseshoe magnet causing the electrical contacts to open. As illustrated in FIG. I, this switch 1 was connected in series with a 6-v0lt dry cell battery 2, a small resistance of about 8.6 ohms 3 and a flashlight bulb 7. The resistance was so placed that when current passed through it the heat produced heated the quaternary antimonide. In operation, when the switch was closed, current flowed through the resistor and the lamp until heat from the resistor caused the antimonide to become sensibly magnetic. When this occurred, the antimonide was attracted by the magnet, opening the electrical contacts and interrupting the current flow. When the antimonide had again cooled to a less magnetic state, it was no longer attracted to the magnet and returned to its original position with the electrical contacts closed and the current flowing. This device thus operated as a blinker light.

The control temperature of such a device can be very precisely and reproducibly adjusted by choice of the proper composition for the magnetic material and remains highly stable over prolonged periods of time. Minor adjustments in control temperature can be provided for, if desired, by adjustment of the gap between antimonide and magnet. Any expedient means may be used to return the armature to its original position. This includes, for example, springs, flexible rods or gravity by proper positioning of the device.

It will be apparent that the position of the antimonide component 6 and the magnetic poles 5 can be interchanged if desired, and devices constructed along these lines have given very satisfactory service as blinker lights. One such device employs a pellet (ca. in diameter and A thick) of a material which undergoes a firstorder transition at 90 C. and has the permanent magnet mounted on a 10:1 lever arm actuating a precision, snap action switch. The switch controls current passing through the blinker light and through the resistor heating the exchange inversion material. The device requires a temperature variation in the transition material of only il C. for operation. Devices of this type have performed satisfactorily for over 500,000 on-off cycles with no evidence of mechanical failure or deterioration in the transition material.

EXAMPLE IV This example illustrates the construction of a radiometer, i.e., a device for measuring radiation intensity (see FIG. II). A disc shaped pellet 16 measuring approximately /2" in diameter by in thickness fabricated from a crystalline powder of manganese-chromiumindium antimonide represented by the formula was employed. Due to the method of fabrication, the easy directions of magnetization, i.e., the tetragonal axes, of the tiny crystals composing the powder were aligned at an average angle of about 60 to the broad faces of the pellet. A small amount of manganese antimonide, MnSb, was randomly distributed throughout the pellet. This pellet was cemented to the center of the tungsten rod 17 having sharply pointed ends. The rod was mounted vertically between two copper bearings 18 so that the pellet was centered between the poles 19 of a permanent magnet having a field strength of about 4800 oersteds. The pellet assumed a position such that its broad faces were parallel to the center line of the pole pieces. One face of the pellet was then illuminated using a microscope illuminator having a lamp of 108 watts. The lamp filament was focused on the face of the pellet. Under these conditions, the pellet was observed to turn through an angle of about 60. When the intensity of the radiation falling on the pellet was decreased by insertion of neutral density filters into the light beam, the angle through which the pellet had turned decreased in a stepwise manner. It was restored to its initial position by turning off the light. Thus, the intensity of radiation falling on the pellet was measured by the angle through which the pellet turned. If desired, a pointer or optical system may be added to the device which together with a suitably calibrated scale will enable intensity of illumination to be read directly.

The resistance of the pellet to turning can be increased, and the range of intensity which can be measured thereby enlarged, by increasing the proportion of conventional magnetic material, e.g., MnSb, in the pellet or by provision of appropriate mechanical components, such as springs.

EXAMPLE V A reciprocating engine is illustrated in this example (see FIG. III). A pellet 20 (about 0.33 g.) of transition material composed of a manganese-chromium-indium antimonide, prepared from a mixture containing the elements in the atomic ratios of 1.8:0.2: .05:0.95 (lower transition temperature 80 C.; maximum saturation induction temperautre 120 C.) was attached to one end of a 4;" diameter phenol formaldehyde resin tube 21 2" in length. To the other end of the tube was attached a similar pellet 22 of Mn Ge (Curie Temperature 45 C.). The tube bearing the pellet was attached at its center perpendicularly to the lower end of a similar tube (8" long) mounted as a pendulum 23 so that the pellets were in a plane of the pendulums swing. One pole (about 1" wide) of a horseshoe magnet 24 having a rated field strength of about 3000 oersteds was placed so that the pole face was about A below the rest position of the pendulum. The pellet of Mn Ge was attracted to the magnetic pole causing the pendulum to be deflected from the vertical. Two projector lamps 25 were arranged so that the light from one was focused on the Mn Ge pellet and from the other on the antimonide pellet. The radiation from the lamps caused the pelets to exceed, respectively, the Curie temperature and the lower transition temperature. When this occurred, the Mn Ge pellet was no longer attracted to the magnetic pole while the antimonide pellet was so attracted and the pendulum was pulled to a position (indicated by dotted lines in FIG. III) with the antimonide pellet close to the pole face. In this position, the pellets were no longer illuminated by the projection lamps and soon cooled sufficiently to pull the pendulum 'back to its former position. The rate of oscillation of the pendulum was controlled by rheostats regulating the current supply to the lamps.

In this device, a reciprocating action is obtained having a power stroke on the heating and cooling cycles, i.e., in both directions of motion. Although the example shows a device powered by two lamps, similar devices powered by only a single source of energy, e.g., the sun, can readily 'be constructed employing suitable shields to block out radiation during the cooling cycle. Sun-powered reciprocating engines possess obvious utility, for example, as power sources in desert locations for pumping water.

EXAMPLE VI This example describes the construction of a magnetic balance which has been employed to determine the variation in magnetic response with temperature of a magnetic material. It will be apparent that by simple modification the balance can be converted to other uses.

As illustrated in FIG. IV the balance consists of an arm supported on a fulcrum 11, one end of the arm is a tube 9 of non-magnetic material, such as glass, through the center of which the leads 10 to a thermocouple are passed. The other end of the arm is a rod carrying adjustable weights 15. Excessive motion of the arm is prevented by stops 14. A closely fitting cap carrying the magnetic material 8 is placed over the open end of the tube 9 in such a position that the thermocouple is in contact with the magnetic material. This end of the arm with attached magnetic material is inserted in a chamber 13 which may be either heated or cooled by conventional means depending upon the temperature range to be employed. Magnetic poles 12 are placed outside this chamber immediately adjacent to the magnetic material in such a position that the glacginetic material experiences a non-uniform magnetic In operation, the weights 15 are adjusted until the attraction of the magnetic field for the magnetic material 8 is just counterbalanced. The temperature of the magnetic material is then changed and the weights again adjusted. By repeating this procedure at a number of temperatures, the effect of temperature on the attraction of the magnetic material by the field can be determined.

By installing an electrical contact on one of the stops l4, and completing a circuit through the arm, the apparatus can be converted to a temperature activated switch. This switch can be used to control heating or cooling means to maintain the temperature of the space within which the magnetic material is located, e.g., the chamber 13 within desired limits.

EXAMPLE VII This example illustrates the direct interconversion of thermal and mechanical energy in a device based upon a transition material. In this device a single crystal of the material was prepared in the form of a parallelepiped 0.2-0.3 inches on each side. One face of the parallelepiped was highly polished and a small V-shaped indentation was made in the opposite face. The parallelepiped was placed at the bottom of a quartz test tube with the face having the V-shaped indentation uppermost and a quartz rod was placed vertically with its lower end engaged in the indentation. The rod was free to move in a vertical direction and the top of the rod actuated the core of a differential transformer. The coils of the transformer were mounted on the top of the quartz tube so that the output of the transformer indicated relative motion between rod and tube. By calibration with precision gauge blocks it was determined that movements of the rod as small as il0 10- inches could be determined. In operation the lower end of the quartz tube containing the transition material was heated or cooled as desired at a rate of about 1 C./min. and movement of the quartz rod produced by thermal expansion or contraction of the transition material was indicated by the output of the differential transformer. The relationship between temperature and motion of the rod at temperatures near the transition temperature is indicated in FIG. V for devices in which motion of the rod is due to changes in dimension parallel to the a and c crystallographic directions, respectively, of a manganese-chromium antimonide having the composition, in atom percent, Mn, 65.5%; Cr, 1.7%; Sb, 32.8%. It will be apparent that motion of the rod can be employed for temperature indication using the device as described and that conversion to a temperature control device can be readily accomplished. By thermostating the transition material, such devices can be modified for use in sensing magnetic field strength.

In another embodiment, a thermometer may be constructed. In this device, a parallelepiped transition material, on expansion and contraction, moves the rod in the same manner as in the above paragraph. However, the differential transformer of the above paragraph is replaced with a Ronchi grating. A Ronchi grating (see Ingalls, Amateur Telescope Making, Scientific American Publishing Co., 1933, pp. 264-270) is a device having uniformly spaced, parallel, opaque lines ruled on a transparent material. customarily, the width of the opaque lines is equal to that of the intervening clear spaces. In this device, a first Ronchi grating is attached to the rod with its surface parallel to the motion of the rod. A second Ronchi grating is permanently mounted with its ruled surfaces in contact and its ruled lines parallel with the first grating. When the opaque lines on one surface match those on the other, light will pass through the gratings. However, if the opaque lines on one surface cover transparent areas on the other, passage of light 'will be more or less blocked depending -on the extent of coverage. Relative motion of the two gratings is produced by dimensional changes in the transition material resulting from changes in temperature. Thus, by measuring the light transmitted through the grating, temperature can be measured. A device so constructed recorded the following Relative Light Intensity based on the corresponding temperature:

Relative light intensity Temperature, C.: (Arbitrary scale) EXAMPLE VIII The compositions useful in devices of this invention are metal-like in temperature dependence of electrical resistance in that resistance increases with increasing temperature at temperatures below and above the temperature at which the first-order transition occurs, i.e., these compositions have in general a positive temperature co efficient of resistance. However, at the transition temperature resistance drops sharply with increasing temperature and one class of device for the interconversion and control of various forms of energy depends for operation on changes in resistivity associated with exchange inversion. Since the first-order transition is influenced by magnetic field and pressure, as well as by temperature, the resistance effect can be applied in devices for the interconversion and control of electrical energy and thermal, magnetic or mechanical energy.

To illustrate, a specimen of transition material was connected to a source of square wave, 70 cycle/second, alternating current of known intensity and two connections were applied near the ends of the specimen for measurement of resistance across the specimen. Resistance was measured at a number of temperatures by adjustment of a calibrated variable resistor in series with the specimen until the voltage drop across the variable resistor equaled that across the specimen. The resistance of the specimen was then equal to and could be read directly from that of the variable resistor. The relationship between resistance and temperature of the specimen is indicated for a typical transition material in FIG. ,VI. From the figure, it is apparent that change in resistance associated with the transition is a measure of temperature, i.e., the foregoing device is, in fact, a resistance thermometer. The resistance effect can also be applied in control circuits where sensitivity to temperature is desired. As further illustrated by the figure, resistance of the transition material is sensitive as well to magnetic field and by the simple expedient of thermostating the exchange inversion composition, resistance devices can be converted for use in sensing or controlling magnetic fields. Resistance also is sensitive to pressure and the devices can be used in pressure-sensing applications.

EXAMPLE IX A temperature sensitive resistor, illustrated in FIG. VII, was fabricated from a transition material corresponding to the formula Mn Cr Sb In The material was first pulverized by grinding in a mortar under liquid nitrogen and powder passing 200 mesh and retained on 270 mesh sieves was employed in the resistor. The powder was spread uniformly over an area ca. 0.5" X 0.5" in size on the surface of a phenolic resin support 50 and pressed at about 40,000 p.s.i. at room temperature to produce a coherent conductive film. A number of such films ranging from 1-5 rnils in thickness were prepared. In order to provide the desired resistor length (about 3"), portions of the film were scraped away leaving the resistor 51 in the form illustrated. Electrical connections 52 were attached to the ends of the resistor with silver paint. One such resistor had a resistance of ohms at 30 C. and a resistance of 94 ohms at 40 C.

In an alternative construction, a piece of manganesec'hromium-indium antimonide was rubbed against a ground glass surface wet with acrylic lacquer. Very fine particles of antimonide remained distributed in the lacquer and a conductive film was formed after the lacquer dried. This film had an electrical resistance of several hundred ohms which was variable with tem perature.

EXAMPLE X A larger motor similar to that described in Example II was constructed using :an aluminum disk 8" in diameter and 0.03" thick as a rotor. The rotor was mounted at its center perpendicular to a horizontal shaft supported at each end in small instrument ball bearings. A powdered (passing 16 mesh) transition material of manganesechromium antimonide was cemented with epoxy resin in a 1" band at the rim on each side of the disk. This antimonide had a transition temperature of 30 C. (80% of the transition being within a range of 4 C.). A mag net having facing pole pieces 1" in diameter, spaced apart, and a field strength of 8000 oersteds, was placed so that the antimonide-bearing rim passed centrally between the pole pieces when the disk rotated. Internally focusing projector lamps of ISO-watt intensity were focused on the antimonide bands just above the pole pieces of the magnet. In one embodiment, the antimonide brands below the magnet were cooled in a tray of cold water; in another embodiment, cooling was achieved with air or water jets directed parallel to the rotor shaft onto the antimonide just below the air gap of the magnet. This motor operated at about 5 rpm. with a peripheral speed of about 10 ft. per minute.

EXAMPLE XI A temperature-responsive magnetic switch (cf. Example III) can be employed in an alarm circuit such as a fire alarm circuit for use in a dwelling. A device illustrative of this application was constructed as indicated in FIG. VIII. In this device, the normally open temperature-sensitive switch 116 was connected to a supply of 110 V. AC. current. A 250-watt heat lamp 115, representing the normal method of using a house circuit (circuit A) was also connected to the same current supply to demonstrate the concurrent normal use of circuit A. For convenience, these connections were made through a wall outlet box 114. The thermally sensitive switch consisted of a magnet 11 7 having a diameter of 0.6" and a length of 0.6" mounted on an insulating support 118. A piece of manganese-chromium-indium antimonide 119 [having the formula Mn Cr In Sb having a transition midpoint at 49 C. (80% range C.) was mounted adjacent to the magnet on a spring loaded lever arm 120. This piece was 0.6" in diameter and 0.2" thick. The lever arm was a piece of cold rolled brass 0.01" thick by 0.44 wide and was carried by a support 121, both lever arm and support being electrically conductive. Electrical connections to the switch were made to the magnet and the support for the lever arm. A second circuit (circuit B) connected to the same source of power supplied current through a manual switch 122 to a small fan 124, and a 25-watt lamp 123 wired in parallel. Each of the circuits A and B was protected from overload by a lS-amp. fuse 112. An alarm bell 111 requiring 0.062 amperes (1775 ohm resistance) for operation was connected to both circuits through 1100 ohm resistors 113. These resistors with the high resistance of the bell itself were sufficient to prevent operation of the bell under normal circumstances. However, after a period of operation in the state illustrated in FIGURE VIII, heat from the heat lamp raised the temperature of the temperature-sensitive switch sufiiciently to cause it to close thereby short-circuiting circuit A. This caused the fuse in circuit A to blow and the alarm bell to ring. However, circuit B was still operable as indicated by lighting of the lamp and operation of the fan when switch 122 was closed. Air circulated by the fan cooled the temperature-sensitive switch causing it to open. Upon replacing the blown fuse with a new fuse, the circuit A was returned to normal operation, whereupon ringing of the alarm bell ceased.

EXAMPLE XII This example illustrates construction of a temperatureresponsive variable condenser utilizing a rod of manganese-chromium antimonide as temperature-sensitive element. The device is illustrated in side elevation in FIG. IX. In one such device the rod 150 had a length of 0.5" and was composed of an antimonide of formula Mn Cr Sb. The rod was surrounded by heating coil 161 and was mounted between ball bearings 151. These bearings were in contact, respectively, with a fixed supporting member 152 of iron and a movable member 153. A fulcrum for the movable member was provided by the ball bearing 154, bearing against support member 155. A spring :156 attached to mounting posts on the end of the movable member remote from the fulcrum and on the support 152 maintained close contact among the ends of rod 150, the ball bearings 151, and members 12 152 and 153. The vertical distance between bearing 154 and the bearing 151 (distance a) was /16 Firmly attached perpendicularly to the movable member was a rigid arm 157, the end of which remote from the area of attachment carried one leaf of a condenser 158. This leaf was an aluminum disk 1%" in diameter and in thickness. The length of the arm 157 between the face of movable member 153 and the center of leaf 158 was 1%" and the vertical distance between the face of the leaf 158 (projected) and the ball bearing 154 was The other leaf of the condenser was a sheet 1 in diameter of copper foil 159 cemented directly beneath leaf 158 to the surface of a glass block 160, mounted on support 152. The condenser leaves were separated by an air-gap serving as the dielectric. Separation of the leaves was variable in response to length changes of rod 150 produced by changes in temperature. Capacitance varied between mmf. and 270 mmf. as a result of these changes.

In one application of this condenser, a second coil was wound on the rod to provide an inductor which was temperature-sensitive by virtue of the change in magnetization of the rod at the transition temperature. The inductor was connected in parallel with the condenser to provide a temperature-sensitive resonant circuit utilizing both magnetic and dimensional changes of the antimonide at the transition temperature. The effect of increasing temperature on the resonant frequency of this circuit is shown in FIG. X.

It will be appreciated that in many devices of this invention, the component which exhibits a sharp increase in saturation induction with rise in temperature will comprise in addition to the material responsive per se for the magnetic behavior of the component, one or more additional materials which provide additional properties necessary or desirable for proper function of the component. For example, the magnetic material may be in the form of particles dispersed in a binder or matrix. The particles may be aligned or randomly oriented. As binder or matrix, any material, solid or fluid, which provides the desired physical properties and resistance to environmental conditions can be used, such as water, mineral oil, plasticized or unplasticized vinyl polymers, natural or synthetic elastomers, epoxy resins, polyamides, polyesters, polyurethanes, plaster of Paris, and the like.

In a ty-picol transition element used in the devices of this invention, the narrow temperatures range over which the first-order transition takes place is about 2-50" C. and is a linear function of the temperature over approximately the central 80% of this temperature range.

The foregoing detailed description has been given for clearness of understanding only and no unnecessary limitations are to be understood therefrom. The invention is not limited to the exact details shown and described for obvious modifications will occur to those skilled in the art.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A device for producing useful work in the form of at least one of mechanical energy and electrical energy from applied heat energy which comprises a structure having an energy-transforming component which undergoes a reversible first-order solid-phase-to-solid-phase transition within a narrow temperature range below its Curie point, said transition resulting in a sharp change in the magnetic saturation induction, electrical resistivity and dimension of said energy-transforming component, said structure having means responsive to at least one of said magnetic saturation induction, electrical resistivity and dimension for converting said applied heat energy to at least one of mechanical energy and electrical energy.

2. The device of claim 1 in which said structure is provided with means to apply heat energy to and from said energy-transforming component.

3. A thermomagnetic generator for producing electrical energy from applied heat energy which comprises, in combination, a frame, an inductor mounted on said frame, a transition material component which undergoes a firstorder solid-phase-to-solid-phase transition within a narrow temperature range below its Curie point resulting in a sharp change in the magnetic saturation induction of said transition material, said transition material component mounted on said frame adjacent said inductor, and means for providing a flow of heat energy to and from said transition material component to cause the temperature of said transition material component to alternately pass through its transition temperature thus producing a sharp and reversible change in the magnetic saturation induction of said transition material component which creates an electrical current in said inductor.

4. The thermomagnetic generator of claim 3 wherein said inductor is a magnetizable material having a conductive wire coiled around it.

5. A motor for producing mechanical energy from applied heat energy which comprises, in combination, a frame, a magnetic member mounted on said frame, a rotatable member connected to said frame, said rotatable member containing a transition material component which undergoes a first-order solid-phase-to-solid-phase transition with a narrow temperature range below its Curie point resulting in a sharp change in the magnetic saturation induction of said transition material component, said transition material component positioned adjacent said magnetic member, means for providing a flow of heat energy to and from a portion of said transition material component to cause the temperature of said portion of said transition material component to pass through its transition temperature thus providing rotation of said rotatable member as said portion of the transition material component is attracted toward said magnetic member.

6. The motor of claim 5 wherein said rotatable member comprises a shaft and a disk perpendicularly mounted on said shaft; wherein the transition material component is positioned around the rim on each side of said disk; wherein the rim of said disk is located centrally between the poles .of said magnetic member, and wherein the flow of heat energy of said means for providing a flow of heat energy is directed to the portion of said transition material component above the poles of said magnetic member.

7. A temperature sensitive electrical switch comprising, in combination, a frame, a magnetic element, a transition material component which undergoes a first-order solidphase-to-solid-phase transition within a narrow temperature range below its Curie point resulting in a sharp change in the magnetic saturation induction of said transition material component, said transition material component and said magnetic element mounted on said frame for relative motion toward and away from each other between a first and a second position, a pair of electrical contacts responsive to said motion of said transition material component and said magnetic element positioned for contact when said component and element are in one of said first and second positions.

8. A device for measuring heat radiation intensity comprising, in combination, a frame, magnetic means mounted on said frame, pivotal means mounted on said frame, a transition material component which undergoes a first-order solid-phase-to-solid-phase transition within a narrow temperature range below its Curie point resulting in a sharp change in the magnetic saturation induction of said transition material component, said transition material component mounted on said pivotal means and positioned between the poles of said magnetic means.

9. A reciprocating engine comprising, in combination, a frame, oscillation means mounted on said frame; a first and a second magnetizable element mounted on opposing sides of said oscillation means, the first said magnetizable element undergoing a first-order solid-phase-to-solid-phase transition within a narrow temperature range below its Curie point resulting in a sharp change in its magnetic saturation induction, the second magnetizable element having a Curie temperature near the first-order transition temperature of said first magnetizable element; magnetic means mounted on said frame and positioned adjacent said oscillation means at a point wherein the magnetic field of the magnetic means includes both the first and second magnetizable elements, and means to alternately heat and cool said first magnetizable element through its first-order transition temperature, and said second magnetizable element through its Curie point, whereby both said magnetizable elements are alternately magnetized and attracted to said magnetic means.

10. A temperature indicating device comprising, in combination, a frame; a transition material component which undergoes a first-order solid-phase-to-solid-phase transition within a narrow temperature range below its Curie point resulting in a sharp change in linear dimension, said transition material component positioned within said frame; connecting means abutting said transition material component, said means responsive to said change in linear dimension of said transition material component; and means to measure the response of said connecting means.

11. A temperature-responsive variable condenser comprising, in combination, a frame, a transition material component which undergoes a firstaorder solid-phase-tosolid-phase transition within a narrow temperature range below its Curie point resulting in a sharp change in linear dimension, said transition material component positioned within said frame; means responsive to said change in linear dimensions, condenser means connected to said responsive means to provide for movement of condenser leaves.

12. A temperature sensitive electrical switch comprising, in combination, a frame, a transition material component connected to said frame which undergoes a firstorder solid-phase-to-solid-phase transition within a narrow temperature range below its Curie point resulting in a sharp change in the magnetic saturation induction of said transition material component, and electrical switch means positioned on said frame to open and close an electrical circuit in response to the change in magnetic saturation induction .of said temperature-responsive element.

No references cited.

MAX L. LEVY, Primary Examiner.

DAVID X. SLINEY, MILTON O. HIRSHFIELD,

Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N00 3,274,405 September 20, 196E Thomas J. Swoboda It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 13, line 29 for "with" read within Signed and sealed this 22nd day of August 1967.

(SEAL) Attest:

ERNEST W. SW'IDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A DEVICE FOR PRODUCING USEFUL WORK IN THE FORM OF AT LEAST ONE OF MECHANICAL ENERGY AND ELECTRICAL ENERGY FROM APPLIED HEAT ENERGY WHICH COMPRISES A STRUCTURE HAVING AN ENERGY-TRANSFORMING COMPONENT WHICH UNDERGOES A REVERSIBLE FIRST-ORDER SOLID-PHASE-TO-SOLID-PHASE TRANSITION WITHIN A NARROW TEMPERATURE RANGE BELOW ITS CURIE POINT, SAID TRANSITION RESULTING IN A SHARP CHANGE IN THE MAGNETIC SATURATION INDUCTION, ELECTRICAL RESISTIVITY AND DIMENSION OF SAID ENERGY-TRANSFORMING COMPONENT, SAID STRUCTURE HAVING MEANS RESPONSIVE TO AT LEAST ONE OF SAID MAGNETIC SATURATION INDUCTION, ELECTRICAL RESISTIVITY AND DIMENSION FOR CONVERTING SAID APPLIED HEAT ENERGY TO AT LEAST ONE OF MECHANICAL ENERGY AND ELECTRICAL ENERGY. 